From the beginnings of recorded history, oceans, streams and lakes have been important sources of food, from which the aquatic animals occupying these bodies of water are gathered. Because of increasing populations, pollution, and over-harvesting in certain areas, these natural resources no longer can meet the growing demand placed on these food sources. Although conservation, enhancements, improved breeding and fish-farming have supplied part of the increased needs, these approaches will be insufficient to meet future world demands for animal protein. Biotechnological advances are having major beneficial effects on our society today, and application of such methods to aquaculture have begun. One approach has been to stimulate the growth of fish by use of growth hormones. For example, human growth hormone and ovine prolactin have been shown to enhance the growth of lower vertebrates (Endocrinology 1973, Vol. 93, No. 4., 960-964). The use of bovine somatotropin to increase the growth of salmon has been extensively described Can. J. Zoo. V. 55, No. 6, 1048-1056, 1977; Bio/Technology V. 3, 643-646, 1985; U.S. Pat. No. 4,689,402. However, not all growth hormones have proven effective. Two studies have found that human placental lactogen had no growth stimulating activity in lower vertebrates (Cohen et al., General and Comparative Endocrinology, 1972, Vol. 18: 384-390; Clarke et al. 1973, Endocrinology, Vol. 93, No. 4, 960-964. Clearly, improved methods for fish production are still desirable.